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Appendix B ______________________________________________________ Calculation Formulas

VAISALA ______________________________________________________________________ 173

APPENDIX B

CALCULATION FORMULAS

This Appendix contains the formulas used for the calculated output

quantities.

The HMT330 series transmitters measure relative humidity and

temperature. From these values dewpoint, mixing ratio, absolute

humidity and enthalpy in normal pressure are calculated using the

following equations:

Dewpoint:

log

















(1)

is the water vapor pressure. The parameters A, m, and T

depend on

temperature according to the following table:

t A m Tn

<0 °C * 6.1134 9.7911 273.47

0 ... 50 °C 6.1078 7.5000 237.3

50 ... 100 °C 5.9987 7.3313 229.1

100 ... 150 °C 5.8493 7.2756 225.0

150 ... 180 °C 6.2301 7.3033 230.0

1) Used for frostpoint calculation if the dewpoint is negative

Mixing ratio:

99.621 

(2)

Absolute humidity:

 68.216

(3)

1 2 ... 168 169 170 171 172 173 174 175 176 177 178

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